The invention relates generally to detector systems and more particularly to a detector system for detecting a target material in a sample.
Fieldable laboratory analytical instruments are necessary in order to provide a device to be used in drug interdiction or explosives detection. For example, one of many narcotics that it would be desirable to detect is cocaine. Methods of detection that "sniff" cocaine or detect the presence of cocaine vapor must be capable of detecting very small quantities of the molecule, or else pre-concentrate the vapor by some known technique. Alternatively, a decomposition product of the cocaine can be detected that has a much larger vapor pressure than the cocaine itself. These decomposition products include various carbonyl compounds.
A number of methods are known for detecting such vapors. These methods include the optical techniques of laser photoacoustic detection and ranging, differential absorption LIDAR and thermal infrared emission imagery. Other laser-based techniques include fluorescence spectroscopy, luminescence spectroscopy and fourier transform infrared spectroscopy. Laser photoacoustic detection and ranging, as well as differential absorption LIDAR, are active techniques that require a pulsed-carbon dioxide or other laser with spectral outputs that match the carbonyl absorptions of interest.
A known device used to detect plastic explosives is manufactured by Science Applications International. This detection system irradiates luggage with thermal neutrons, some of which are captured by the atoms of the luggage and its contents. These atoms then emit gamma rays which reveal the chemical structure of the objects irradiated.
All of the above-mentioned techniques have a number of limitations and disadvantages. For example, in some of these techniques the device can only detect those particular targets it has been pre-tuned to detect; it cannot analyze everything that passes through its sample area. Furthermore, some of these devices utilize single mode sensing in which the sample to be analyzed must come to a rest in the sample area, inefficiently slowing down the detection process.